Fix integer overflow in utf{16,32}_to_utf8_length am: c17624db31 am: 3065de2c86  -s ours am: c282fe5c2c  -s ours
am: 47dfd5afee  -s ours

Change-Id: I07a4521a0c2b99e71b41b26294be5b9cf1c8b817